Effects of substrate surface treatments on hybrid manufacturing of AlSi7Mg using die casting and selective laser melting

Abstract

To balance the manufacturing cost and customizability of automotive parts, a hybrid manufacturing process combining die-casting and selective laser melting (SLM) is proposed: starting with a conventional cast substrate, SLM is utilized to add additional geometric elements on top of it. For this hybrid process, the first priority is to prepare a substrate surface suitable for the subsequent SLM addition of the top-on elements. In this study, the original cast surface of AlSi7Mg was processed by sandblasting, wire electro-discharge machining, and laser remelting, respectively. Then, additional AlSi7Mg components were built on both the original cast and treated surfaces through SLM. After hybrid builds, these surfaces and resultant interfaces were examined by optical and scanning electron microscopes. Results indicate that the defect-free metallurgical joint between the cast and additively added parts can be formed on all surfaces except for the one processed by electro-discharge machining. The observed epitaxial grain growth crossing the interface implies a strong connection between the cast and the SLMed component. Despite these benefits, also mismatches in microstructure, residual stress level and element distribution between the two parts are identified. After a comprehensive assessment, laser remelting with no additional machining is recommended as the optimal surface treatment preceding SLM fabrication, because of its user-friendly operation, low cost, and high industrial feasibility.